On 27/03/2023 5:13 pm, George Dunlap wrote: > A recent xentrace highlighted an unhandled corner case in the vcpu > "start-of-day" logic, if the trace starts after the last running -> > non-running transition, but before the first non-running -> running > transition. Because start-of-day wasn't handled, vcpu_next_update() > was expecting p->current to be NULL, and tripping out with the > following error message when it wasn't: > > vcpu_next_update: FATAL: p->current not NULL! (d32768dv$p, runstate > RUNSTATE_INIT) > > where 32768 is the DEFAULT_DOMAIN, and $p is the pcpu number. > > Instead of calling vcpu_start() piecemeal throughout > sched_runstate_process(), call it at the top of the function if the > vcpu in question is still in RUNSTATE_INIT, so that we can handle all > the cases in one place. > > Sketch out at the top of the function all cases which we need to > handle, and what to do in those cases. Some transitions tell us where > v is running; some transitions tell us about what is (or is not) > running on p; some transitions tell us neither. > > If a transition tells us where v is now running, update its state; > otherwise leave it in INIT, in order to avoid having to deal with TSC > skew on start-up. > > If a transition tells us what is or is not running on p, update > p->current (either to v or NULL). Otherwise leave it alone. > > If neither, do nothing. > > Reifying those rules: > > - If we're continuing to run, set v to RUNNING, and use p->first_tsc > as the runstate time. > > - If we're starting to run, set v to RUNNING, and use ri->tsc as the > runstate time. > > - If v is being deschedled, leave v in the INIT state to avoid dealing > with TSC skew; but set p->current to NULL so that whatever is > scheduled next won't trigger the assert in vcpu_next_update(). > > - If a vcpu is waking up (switching from one non-runnable state to > another non-runnable state), leave v in INIT, and p in whatever > state it's in (which may be the default domain, or some other vcpu > which has already run). > > While here, fix the comment above vcpu_start; it's called when the > vcpu state is INIT, not when current is the default domain. > > Signed-off-by: George Dunlap <george.dun...@cloud.com>
Acked-by: Andrew Cooper <andrew.coop...@citrix.com>
